Slide shoe and piston arrangement

ABSTRACT

In a hydostatic rotary pump or motor having a cylinder block with cylinders, pistons are mounted which are provided with slide shoes engaging an eccentric annular actuating guide means so that the pistons are reciprocated. Each piston has a spherical end face in sliding contact with a spherical inner slide shoe face having the same radius and center. Mechanical connecting means mount the slide shoe on the piston for angular movement about the center.

United States Patent 1191 Aldinger et al.

1451 Aug. 13, 1974 SLIDE SHOE AND PISTON ARRANGEMENT 2,918,338 12/1959 Grad 92/157 3,223,046 12/1965 Eickmann .1 92/58 [751 lnvenmrs' ulrfch Aldmgel" Gunter Kersten 3,273,344 9/1966 Christensen et al. 60/19 Emll Kmdel, all Of Stuttgart 3,291,068 12/1966 Wiggermann 91/488 7 Germany 3,295,459 1/1967 91/488 Assignee: Robert Bosch GmbH, Stuttgart, 3,663,125 11/1970 Freemann 91/498 Germany FOREIGN PATENTS OR APPLICATlONS [22] Filed: Apr. 10, 1972 638,758 6/[950 Great Britain 92/58 246,097 7/1909 Germany 91/498 [21] Appl. No.: 242,485 1,653,506 10/1970 Germany 91/491 [30] Foreign Application Priority Data Prima'y Examiner-William Freeh Apr. 17,1971 Germany 2118712 Attorney Agent or Smker 52] US. Cl. 91/488, 92/258 ABSTRACT [51] I131. C1. F01) 13/04 In a hydostatic rotary pump or motor having a cy]in 1 Fleld of Search 492, 497, der block with cylinders, pistons are mounted which 53 are provided with slide shoes engaging an eccentric annular actuating guide means so that the pistons are [56] References C te reciprocated. Each piston has a spherical end face in UNITED STATES PATENTS sliding contact with a spherical inner slide shoe face 1 876 833 9/1932 Benedek 91 492 having the Same radius and cemefi Mechanical 1:930:163 10/1933 necting means mount the slide shoe on the piston for 2,033,464 3/1936 angular movement about the center. 2,752,214 6/1956 2,901,979 9 1959 Henrichsen 91/488 4 clam! 14 Drawmg II 5 8 V 26 2 2 7 W 1 1 79- i I 'K 25G 28 28(1 20 2 PAIENILMUC 1 32914 T 3.828.653 sum am 3 .K @Kwm my ON m t SLIDE SHOE AND PISTON ARRANGEMENT BACKGROUND OF THE INVENTION The invention is concerned with an improvement of a slide shoe and piston means whose piston has a convex cylindrical or spherical piston end face in sliding engagement with a concave inner slide shoe face which is either cylindrical or spherical, and has the same radius of curvature.

The German 08. 1,962,546 discloses a slide shoe and piston means for a radial piston machine such as a pump or motor, in which a piston, which is guided in a cylinder, abuts with a spherical end face, on a spherical face of a slide shoe. A compression spring biasses the piston toward the slide shoe which slides along an eccentric annular actuating ring so that the slide shoe effects a reciprocating motion of the piston in the cylinder for increasing and reducing the volume of the cylinder chambers.

The construction of the prior art has the disadvantage that the piston end can slide out of the spherical face of the slide shoe, if the frictional resistance which the slide shoe encounters on the guide face of the actuator ring, is greater than the opposing component of the resultant force of the fluid pressure and the spring. Furthermore, the re-engagement of the piston by the slide shoe after a previous separation causes substantial noise, and may result in damage to the engaging faces.

SUMMARY OF THE INVENTION It is one object of the invention to provide a slide shoe and piston means for a rotary hydrostatic machine, such as a pump or motor, which overcomes the disadvantages of the prior art, and reliably operates at high speed and pressure.

Another object of the invention is to connect the piston shoe with the piston by angularly movable attaching means of predetermined length so that the inner slide shoe face remains in sliding contact with the piston end face even at high friction encountered by the slide shoe.

The objects of the invention are obtained by positively and mechanically connecting the slide shoe with the piston by attaching means so that the slide shoe cannot separate from the piston.

Preferably, the attaching means includes a connecting member of predetermined length having a spherical head portion mounted on an annular spherical seat in a bore of the cylinder for angular movement about the center of the spherical piston end face and inner slide shoe end face, and having another end portion fixedly secured to the slide shoe.

In a preferred embodiment of the invention, the spherical end portion of the connecting member engages an annular spherical seat formed in an annular member which has an annular shoulder on which a spring abuts which is supported on an annular shoulder so that the slide shoe and the piston are angularly movable relative to each other about the common center of the inner slide shoe face and piston end face.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF TI-IEDRAWING FIG. la is a sectional view taken on line II in FIG. lb, and illustrating a first embodiment of the invention;

FIG. lb is a fragmentary cross-sectional view perpendicular to the axis of rotation of a rotary hydrostatic machine;

FIG. 2a is a fragmentary sectional view taken on line II-II in FIG. 2b and illustrating a second embodiment of the invention;

FIG. 2b is a cross-sectional view of the embodiment of FIG. 2a;

FIG. 3a is a fragmentary sectional view taken on line lIIlII and illustrating a third embodiment of the invention;

FIG. 3b is a fragmentary cross-sectional view illustrating the embodiment of FIG. 3a;

FIG. 4a is a fragmentary sectional view taken on line IV-IV in FIG. 4b, and illustrating a fourth embodiment of the invention;

FIG. 4b is a fragmentary cross-sectional view illustrating the embodiment of FIG. 40;

FIG. 5a is a fragmentary cross-sectional view taken on line VV in FIG. 5b and illustrating a fifth embodiment of the invention;

FIG. 6a is a fragmentary sectional view taken on line Vl-Vl in FIG. 6b, and illustrating a second embodiment of the invention;

FIG. 6b is a fragmentary cross-sectional view illustrating the embodiment of FIG. 6a;

FIG. 7a is a fragmentary sectional view taken on line VII-VII in FIG. 7b and illustrating a seventh embodiment of the invention; and

FIG. 7b is a fragmentary cross-sectional view of the embodiment shown in FIG. 7a.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The drawing illustrates the invention applied to a radial piston machine which includes a rotor l rotatable about an axis of rotation and having a plurality of cylinders in which slide shoes and piston means are mounted, respectively for radial movement. The slide shoes slide on the inner face of an eccentric actuating guide ring 6 so that the pistons are reciprocated in cylinders to expand and contract the working chambers, as is known to those skilled in the art.

Referring particularly to FIGS. la and lb, a slide shoe 4 has an outer curved face 4a cooperating with the inner annular eccentric face 5 of the actuator ring 6 which has annular portions 8 and 9 confining a flange 4b portion of slide shoe 4 so that the outer face 4a cannot separate from the actuator ring 6. The piston 3 has a stepped inner bore 12 forming an annular seat 11 of frusto-conical configuration. Piston 3 has a spherical end face 18 having a center M and a radius R. The piston end face 18 is convex, and in sliding contact with the concave spherical inner slide shoe face 17 which has the same radius R and a center coinciding with the center M. An attaching means 7 includes a substantially U-shaped spring 7 having apair of legs 7 with transverse end portions 7" which abut on a shoulder 16 of a recess 14 which is connected with an opening 13 passing through the slide shoe 4 and opening into the narrow portion of the stepped bore 12 in piston 3. Attaching means 7 has a circular yoke portion 10 mounted in the seat 11 for angular movement, and since the center of the circular yoke portion 10 coincides with the center M, attaching means 7 can perform an angular movement about the center M together with the slide shoe 4 while the inner concave spherical slide shoe face 18 slides on the convex spherical piston end face 17. The distance between the portions 7' and the yoke 10 is accurately selected so that the attaching means 7 positively prevent separation of the faces 17 and 18 due to friction encountered by the outer face 4a of slide shoe 4 on the inner surface of the eccentric actuator ring 6.

The convex spherical piston end face 17 has a flat portion 17' forming with the inner slide shoe face 18 a pressure recess 17". Due to the equality of the radii R of the spherical faces 17 and 18, the center M is located in the cylinder bore 2 even in the position in which the piston 3 farthest projects out .of the cylinder bore 2. In this manner, sliding contact between the faces 17 and 18 is assured, while relative angular movement between piston 3 and slide shoe 4 is possible.

The pressure chamber 17 communicates through the stepped bore 12 in piston 3 with the cylinder 2, and has the same pressure so that the pressure acting on the flat portion 17 is equal to the pressure acting in cylinder 2 on piston 3 so that the specific pressure at the faces 17 and 18 is small. The friction forces during angular displacement of the piston 3 relative to slide shoe 4 are small, so that fast starting of the machine and high efficiency are obtained.

Due to the small wall thickness of piston 3, the piston expands upon increased pressure, which prevents an increase of the leakage losses due to the increased pressure by reducing the width of the gap between piston 3 and cylinder 2.

The embodiment of FIG. 2a operates on the same principle as the embodiment of FIG. 1a. A stepped bore 21 passes through slide shoe 20 and opens into a bore 23 in piston 22 which has an annular spherical seat 25. The stepped bore 21 in the slide shoe 20 includes a pressure recess 19, and a shoulder 210 on which the head 26a of a screw 26 abuts. The screw 26 projects into the bore 23, and carries at the end a spherical nut 28 which is adjusted .on the screw 26 to slidingly abut the spherical seat while holding the faces 17 and 18 on sliding contact. The center of the spherical head 28 coincides with the center of curvature of the spherical faces 17 and 18, so that the slide shoe 20 can turn about the center of the annular spherical seat 25 while the spherical faces 17 and 18 slide on each other.

The piston end face 17 is provided with a flat portion 22 which forms with the concave slide shoe face 18, a pressure chamber 22" performing the function described with reference to the pressure chamber 17" in FIGS. 1a and lb. A longitudinal bore passes through the screw 26 and head 26a. and ends in a bore 28a of the spherical head 28 so that a balancing recess 19 on the outer face of slide shoe 20 communicates through ducts 27, 28, 28a with the respectivecylinder 2.

After the length of the attaching means 26, 28 has been adjusted by means of the spherical nut 28, the thread may be deformed to permanently secure nut 28 to screw 26 to prevent a loosening of nut 28 during operation of the machine. The threaded connection permits a very fine adjustment of the clearance between the inner spherical slide shoe face 18, and the spherical piston end face 17.

In the embodiment of FIG. 3a, the slide shoe 30 has a rod portion 31 projecting into the stepped inner bore 32 in piston 29. The stepped inner bore 32 forms an annular frusto-conical shoulder 35 which serves as a seat for an annular member 33 which is slidably guided on the slide shoe rod 31, and has an outer annular spherical face 34 in contact with the annular seat 35 due to dished springs 37 which abut the annular member 33 and also a spring ring 36 secured to slide shoe rod 31. The resilient force of springs 37 urges the spherical inner face 30 of slide shoe 30 into contact with the spherical cylinder end face 17, while permitting relative angular movement between slide shoe 30 and piston 29 about the center of the spherical faces 30 and 17 which coincides with the center of the spherical face 34 of the annular member 33 cooperating with the frustoconical seat 35. In the illustrated operative position, the dished springs 37 are pretensioned. A longitudinal bore passes through the slide shoe 30 and slide shoe rod 31 to connect the pressure balancing chamber 14 in the outer face of slide shoe 30 with the bore 32 of piston 29 and with the cylinder 2. I

The spherical piston end face 17 has a flat face portion 29 forming with the concave spherical face 30 of the slide shoe a pressure chamber 29".

Due to the action of the springs37, slide shoe 30 and piston 29 are held in the correct position, which prevents wear of the engaging spherical faces 30' and 17. The projecting rod portion 31 assures the movement of slide shoe 30 together with piston 29 during piston movements. The pressure acting on the flat face 29' in the pressure chamber 29" obtains an almost perfect equilibrium of the forces acting on the piston 29 so that the forces transmitted to the slide shoe 30 are small, resulting in small pressure and small frictional force acting on the faces 30 and 17.

In the embodiment of FIGS. 4a and 4b, the piston 39 has a stepped bore 42 which has a narrow throttle portion 42 opening into cylinder 2. The tubular wall of piston 39 has diametrical bores 43 in which a shaft pin 44 is mounted whose axis coincides with the centerof the spherical piston end face 17 and of the spherical slide shoe face 41' of slide shoe 41. A connecting member 46 has a bearing bore and is mounted on the shaft pin 44 for angular movement about an axis passing through the center of curvature of faces 41 and 17. Connecting member 46 has a flange end portion 47 which abuts an annular shoulder 48 in the outer face of slide shoe 41. Piston 39 has on the spherical face 17, a flat face 39' which defines with the inner spherical face 41' of slide shoe 41, a pressure chamber 39" communicating with the stepped bore 40 and through the throttle passage 42 with cylinder 2. Attaching means 44, 46, 47 holds slide shoe 41 in a position in which the spherical or cylindrical faces 41', 17 can slide on each other.

In the embodiment of FIGS. 5a and 5b, the piston 48 has an axial stepped bore 49 including a cylindrical portion 49b opening on the cylinder, and the frustoconical portion 49a opening into the convex spherical piston end face 18. Between bore portions 49a and 4%, an annular shoulder is formed which has a planar annular face 50 and an adjacent annular spherical seat 51 whose center coincides with the center of the spherical piston end face 17. A hollow connecting member 52 has a rivet head 52a secured to slide shoe 54, and another end portion 53 with an annular spherical face 53a slidingly engaging the annular spherical seat 51 so that connecting member 52 turns about the center of the spherical convex piston end face 17 together with slide shoe 45. The length of the connecting member is accurately selected to permit angular movement of slide shoe 54 without separation of the spherical faces 17 and 54a. A coil spring 55 is located in the respective cylinder 2, abutting the bottom of the same, and abutting also the planar annular shoulder 50 of the stepped bore 49 so that the spherical piston end portion 17 is pressed against the convex spherical slide shoe portion 54a. A flat face portion 48 forms with the spherical inner slide shoe face 54a, a pressure chamber 48".

The rivet connection of connecting member 52 with slide shoe 54, assures a reliable transporting of the slide shoe 54 by the piston 48 during rotation of the rotor, while the compression spring 55 compensates wear on the slide faces 17 and 54a. A throttle passage 56 passes through connecting member 52 and connects the recess 19 through the stepped bore 49 with cylinder 2.

In the embodiment of FIG. 6, piston 57 has a stepped bore 58 with an annular shoulder 61 on which the annular flange of a frusto-conical bushing 59 abuts, held by the force of a coil spring 60 which abuts at the remote end on the bottom of cylinder 2. A bolt 62 is secured by head 62a in a recess 65 of the slide shoe 66, and projects into the stepped inner bore through the shoulder 61 and the frust-conical bushing 59. The diameter of the smaller opening of the frusto-conical bushing 69 is the same as the diameter of bolt 62 so that a joint is formed permitting angular movement of bolt 62 with slide shoe 66 about the center of the spherical piston end face 17 and of the spherical inner slide shoe face 66a. Bolt 62 is provided with a longitudinal duct 63 connecting the pressure fluid recess 64 with the stepped bore 58 and cylinder 2.

The spherical piston end portion 17 has a flat face 57 forming with the inner slide shoe face 660, a pressure chamber 57".

At the beginning of the operation, piston 57 is pressed by the force of spring 60 and also by the centrifugal force and by hydrostatic fluid pressure, against the concave spherical inner slide shoe face 66a. When the slide shoe encounters great resistance, which is greater than the force applied by the piston 62 to the slide shoe 66 for moving the same along the eccentric inner annular surface of actuator ring 6, piston 57 yields toward the cylinder block 1 until the bolt 62 abuts the inner surface of the conical bushing 59, as illustrated in FIG. 6b so that movement of slide shoe 66 with rotor 1 is assured. The narrow opening at the end of frusto-conical bushing 59 forms a bearing for bolt 62 permitting angular movement about the center of the spherical piston end face 17 so that relative sliding of the spherical faces 17 and 66a can take place without separation.

In the embodiment of FIGS. 7a and 7b, the piston 72 has a stepped bore 73 forming an annular planar shoulder 79 on which a dished spring 78 abuts. An annular member 77 abuts spring 78, and has an inner annular spherical seat 74 whose center coincides with the center of the spherical piston end face 75, and with the center of the spherical concave inner face 80 of the slide shoe 70. A connecting member 71 has a head portion fixedly secured in a recess of slide shoe 70, and another end portion formed with an annular spherical face 74 in sliding contact with the annular spherical seat 77 of annular member 76. The spring 78 is pretensioned and urges annular member 77 to the right as viewed in FIG. 7b so that slide shoe is pressed with its spherical face 80 against the spherical piston end face 75. As shown in FIG. 7a, a longitudinal duct 81 connects the recess 82 in the outer face of slide shoe 70 with the stepped piston bore 73 and with cylinder 2.

During rotation of the rotor cylinder block 1, the friction force between the slide shoe 70 and the piston 72, caused by spring 78, effects the transporting of slide shoe 70 by the piston 72. If slide shoe 70 encounters resistance which is greater than the transporting force, piston 72 yields against the action of spring 78 until the annular member 76 abuts the wall 73a of the stepped bore 73 and is positively taken along with the piston.

While the embodimentsof FIGS. 1a to 7b are shown in connection with the radial piston machine having an eccentric annular actuator ring, it will be understood that the invention can also be applied to an axial piston machine in which the actuating guide element is a swash plate. A rigid connection between piston and slide shoe is not absolutely necessary.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of slide shoe and piston arrangements differing from the types described above.

While the invention has been illustrated and described as embodied in a slide shoe and piston means in which the slide shoe is connected with the piston for angular movement about the center of spherical, slidably engaged, piston and slide shoe faces, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

We claim:

1. In combination with a rotary hydrostatic machine including a cylinder block element having cylinders, and an actuating guide element, one of said elements being rotatable relative to the other element; a slide shoe and piston arrangement comprising a piston having a stepped inner bore forming a curved seat, said piston being movable in one of said cylinders between ad-' vanced and retracted positions, and ending in a curved convex piston end face having a predetermined radius, and a center of curvature located in said cylinder in said retracted and advanced positions; a slide shoe having an outer face slidingly engaging said actuating guide element, and an inner curved concave slide shoe face having the same radius and center of curvature as said piston end face; and attaching means having a first end portion mounted in said curved seat of said piston for angular movement about said center, and a second end portion fixedly secured to said slide shoe, said end portions being spaced a predetermined radial distance so that said slide shoe and attaching means can move about said center while said inner slide shoe face slides on said piston end face.

2. Slide shoe and piston means as claimed in claim 1, wherein said end portions of said attaching means are fixedly connected to each other.

3. Slide shoe and piston means as claimed in claim 1, wherein said piston has a stepped inner borc forming an annular spherical seat; wherein said slide shoe has a recess in said outer face and an opening connected with said recess and forming a shoulder; and wherein attaching means includes a screw passing through said opening and having head located in said recess abutting said shoulder, and a spherical nut screwed onto said screw and mounted in said seat for angular movement about said center.

4. Slide shoe and piston means as claimed in claim 1, wherein said slide shoe has a recess in said outer face thereof; and wherein said connecting member has a throttle passage connecting said recess with said cylin- 

1. In combination with a rotary hydrostatic machine including a cylinder block element having cylinders, and an actuating guide element, one of said elements being rotatable relative to the other element; a slide shoe and piston arrangement comprising a piston having a stepped inner bore forming a curved seat, said piston being movable in one of said cylinders between advanced and retracted positions, and ending in a curved convex piston end face having a predetermined radius, and a center of curvature located in said cylinder in said retracted and advanced positions; a slide shoe having an outer face slidingly engaging said actuating guide element, and an inner curved concave slide shoe face having the same radius and center of curvature as said piston end face; and attaching means having a first end portion mounted in said curved seat of said piston for angular movement about said center, and a second end portion fixedly secured to said slide shoe, said end portions being spaced a predetermined radial distance so that said slide shoe and attaching means can move about said center while said inner slide shoe face slides on said piston end face.
 2. Slide shoe and piston means as claimed in claim 1, wherein said end portions of said attaching means are fixedly connected to each other.
 3. Slide shoe and piston means as claimed in claim 1, wherein said piston has a stepped inner bore forming an annular spherical seat; wherein said slide shoe has a recess in said outer face and an opening connected with said recess and forming a shoulder; and wherein attaching means includes a screw passing through said opening and having head located in said recess abutting said shoulder, and a spherical nut screwed onto said screw and mounted in said seat for angular movement about said center.
 4. Slide shoe and piston means as claimed in claim 1, wherein said slide shoe has a recess in said outer face thereof; and wherein said connecting member has a throttle passage connecting said recess with said cylinder. 